This invention relates to one-way clutches, which are common components in rotary mechanical power transmission systems. More specifically, the invention is an improvement on the planar xe2x80x9cstrutxe2x80x9d type of one-way clutch as first seen in U.S. Pat. No. 5,070,978 and subsequent improvements sold under the Trademark, xe2x80x9cMechanical Diodexe2x80x9d (TM).
One-way clutches or OWC""s as they are commonly known provide a variety of different functions in rotary power transmission systems such as safety devices for helicopter auto-rotation, hold-backs for conveyor systems and as shift components in automotive transmissions to name a few.
All OWC""s including the planar type, require significant lubrication in high-speed applications to prevent wear and damage due to friction. The presence of fluid is more critical in the planar type of OWC as the lubrication serves as an active component in stabilizing the behavior of the strut when overrunning in excess of the maximum dry speed. This speed varies according to the actual geometry of the clutch but has been experimentally established at xcx9c2,000 RPM for the general example shown later in this discussion. In very high speed applications, all OWC""s require a copious amount of lubricant flow to carry off waste heat generated as a consequence of fluid shear.
One problem currently not well addressed in all OWC""s is in the rare occasions where system failure, contamination or momentary inertial forces cause a momentary cessation of lubricant flow. While damaging to all types of OWC""s, this event can cause a rapid, catastrophic failure in a planar OWC.
In the example of helicopter auto-rotation this is very serious since the reason this safety feature might be needed is in the event of sudden loss of oil and the subsequent seizing of the engine and gear train.
Refinements have been made on the original strut geometry of planar OWC""s that improve this situation so as to give a longer survivable time in an oil starved condition such as in U.S. Pat. No. 5,597,057 and U.S. Pat. No. 6,116,394. While this material shows an improvement, the techniques disclosed do not addrss the lack of stability of the strut but merely seek to restrain its resultant poor behavior. U.S. Pat. No. 6,116,394 describes the problem where unconstrained and deprived of fluid, the rear portion of the strut can enter the space of a notch and Impact with high force causing damage. U.S. Pat. No. 5,597,057 treats this by elongating the ears on the strut so that they protrude past the notch and will impact against the face of the notch plate rather than on a ramp of a notch. U.S. Pat. No. 6,116,394 shows a different strategy. It attempts to trap one edge of the strut between its pocket and the face of the notch plate so as to constrain its rotation in the event of oil loss.
In the particular case of an OWC with one member stationary and the other rotating, there is a simple solution that allows high-speed over running in the absence of fluid without strut failure. It is one purpose of this invention to show such a method.
Another purpose of this invention is to address the root cause of this failing in planar OWC design and remove the stimulus for bad behavior in those situations where the clutch is deprived of operating fluid. This is done by biasing the strut out of contact with the notch plate during overrun by utilizing the outward force generated by the strut carried by its pocket plate and to force a reaction with a cooperating feature on the pocket plate to counteract the bias of the engagement spring.
It is important to describe the sequence of events that cause catastrophic strut failure during high-speed, no-oil overrun in these prior art devices. FIG. 1 shows the general construction of a strut type planar clutch comprised of notch plate 7, pocket plate 2, strut 3 and spring 9. FIGS. 2 through 4 show sequential cross-sectional views of a single strut 3 according to the prior art during over run with no oil.
First, according to FIG. 2, the strut 3 is biased upward into a passing notch 10 by its spring 9. Next, the strut tip 11 is struck a glancing blow by the passing ramp of notch 10, imparting a rotational moment about the strut 3 center of mass and also generating a downward thrust to the strut 3. It is important to note that this initial impact is relatively small in magnitude. Now looking to FIG. 3, the strut impacts the bottom of its pocket 13, rebounding upward and pivoting about the point of contact as can be seen in FIG. 4. The rear of the strut 3 continues to rise into an adjacent notch 10. Finally, the rear of the strut 12 is struck smartly by that notch 10 ramp, imparting a large shock to the strut 3.
It is this last impact in the series that imparts the damaging forces and velocities to the strut 3. Since this last impact requires the strut 3 to be in an orientation contrary to the bias of the spring 9, it does not happen normally but only as a consequence of the entire sequence of FIGS. 2 to 4 as described above and only in the absence of surrounding fluid.